European investigators have shut down an encrypted communication service that was used as a secure channel for organized crime, particularly in the drug trade, and arrested 48 people, German authorities said Monday.

More than 70 properties were searched in Germany, the Netherlands, Belgium and Poland on Friday, when the arrests were made, the criminal police office in the western German state of Rhineland-Palatinate said in a statement.

It said that those arrested were users, operators and administrators of the communication service, Exclu.

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The detentions resulted from an investigation launched in 2020, which had its roots in the shutdown the previous year of a former military bunker in western Germany that hosted sites dealing in drugs and other illegal activities. Those included Exclu.

German authorities said Exclu was offered to users as a smartphone app, with a six-month license costing $860. It had an estimated 3,000 users — 750 of them in the Netherlands, where police also were involved in the investigation.